As is well known, graft polyblends of rubbers with various vinylidene polymers have advantages in providing compositions of desirable toughness, chemical resistance and good formability. ABS polyblends have proven particularly advantageous in many application, and modifications of such ABS polyblends include the substitution of alkyl acrylate esters for a portion of the vinylidene monomer components, variations of the ratio of styrene-type and acrylonitrile-type monomers and the use of saturated rubbers such as acrylate rubbers as the substrate for the graft.
In the U.S. Pat. No. 3,509,238 granted Apr. 28, 1970 to Aubrey and Jastrzebski, there is disclosed and claimed an ABS-type polyblend containing graft copolymers having distinct degrees of grafting to provide a highly desirable balance of properties, the lowly grafted polymer apparently tending to cluster and simulate a larger particle size graft copolymer to provide a very high degree of impact resistance. In U.S. Pat. No. 3,509,237 granted to Norman E. Aubrey on Apr. 28, 1970, there is disclosed and claimed an ABS-type polyblend wherein there are graft copolymer particles of relative small size and other graft copolymer particles of relatively large size. A relatively small amount of the large particles provides greatly enhanced impact resistance in combination with the small particles while the larger amount of the smaller particles extends the effectiveness of the large particles to levels which larger amounts of either do not provide. Additionally, the volume of small particles masks the undesirable effects of the larger particles upon the overall balance of properties.
The concepts of the aforementioned patents have been widely employed in commercial compositions. In the commercial use of the concept of the latter of the above mentioned patents, the large particle component has been provided by a mass/suspension polymerization process and the smaller particle component has been provided by an emulsion polymerization process. There has been a desire to prepare both components by emulsion processes, mostly desirably in a single reactor, in an effort to minimize costs. However, grafts of purchased latices having a large average particle size have not proven so effective as the mass/suspension graft copolymers.
More recently, U.S. Pat. No. 3,652,721 to Dalton et al. has disclosed a process wherein small rubber particles are grafted in emulsion and combined with a grafted large agglomerated rubber particle to form ABS polyblends having a bimodal rubber particle size distribution. The product is considered to have high utility, however, the several separate batch operations to form the two sized modes of the rubber particles reduces process efficiencies. U.S. Pat. No. 3,663,656 to Ford et al. discloses a similar process wherein small rubber particles are grafted in a first emulsion followed by the addition of an emulsion of large rubber particles to the first emulsion and a completion of the grafting of the large particles to provide an ABS polyblend having a bimodal distribution of grafted rubber particles. Here again the separate batch steps reduces process efficiencies.
It is an object of the present invention to provide a novel polymerized polyblend of emulsion polymerized graft copolymers having different particle sizes and affording a highly desirable balance of properties.
It is also an object to provide a process for making such polyblends of emulsion graft copolymers which is relatively simple and economical in operation and which is adapted to facile variation to accommodate variations in particle size and grafting level.
Another object is to provide such polyblends which may be produced in a single reactor and in a single graft polymerization cycle.